Vale Cassini: Fiery Farewell to a Heroic Undertaking

Vale Cassini: Fiery Farewell to a Heroic Undertaking

September 22, 2017

This week’s circular message tells a remarkable story of imagination, intelligence, and persistence that began before the birth of any current ISF student and even pre-dates some of our parents: it came to an end last Friday.

On October 15, 1997, a Titan IVB/Centaur rocket launched from Cape Canaveral in the United States to send an orbiter named ‘Cassini’ on an eight-billion-kilometre journey of discovery to Saturn. Last Friday, just one month short of 20 years, the Cassini orbiter came to a fiery end as it plunged into the outer atmosphere of Saturn at a speed of over 111,000 kilometers per hour.

Cassini’s journey has been a remarkable one for the global teams of scientists, technicians, administrators, and the many amateur followers who have planned and executed its extraordinary mission. Commencing as an ambitious concept in Europe in 1982, it gradually captured the imagination and attention of government agencies, notably NASA. By mission’s end, 27 nations had contributed to the Cassini saga; more than 2.5 million commands from the Control Center guided the Cassini mission; Cassini completed just under 300 orbits of Saturn. By all measures, Cassini has been an amazing photographer: over 450,000 images were captured over its 20-year mission. Nearly 4,000 scientific papers have been written to date on the many wondrous discoveries transmitted back to earth by Cassini in the form of 635 Giga bytes of data. Cassini discovered six unknown moons, solved the 300-year old mystery of two-toned Iapetus, and discovered lakes, rivers, and oceans beyond our own world.

On Enceladus, the sixth largest moon orbiting Saturn, during 23 flybys, Cassini discovered massive liquid oceans under a 30-kilometer deep icy crust. It captured exceptionally detailed images, including fountains of salt water streaming into space. We now believe that Enceladus is the one place in the Solar System outside of Earth that offers an environment potentially hospitable to microbial alien life.

On Titan, Saturn’s largest moon, Cassini discovered the only other place in the Solar System known to have liquid surface lakes and seas. Stretching for hundreds of kilometres, with depths reaching hundreds of meters, these liquid methane and ethane seas have been a major surprise arising from Cassini’s mission. The analogies with our own planet were remarkable, as scientists were able to detect clouds drifting over wide range of eroded landforms created by movements of flowing liquid across the surface of Titan. It is a landscape that has already prompted planning for a return mission, to launch in 2020.

The final image transmitted by Cassini, taken as it began to encounter the first wisps of Saturn’s hydrogen-rich atmosphere, shows the eventual crash site.

The decision to ‘crash and burn’ rather than powering down Cassini to an eternal cold electronic silence is a remarkable footnote in this story. NASA, excited at the prospect of future missions to study non-terrestrial lifeforms, feared the potentially disastrous impact of contamination, carried by Cassini from Earth. The cleansing fire of an atmospheric encounter was chosen to preserve the pristine ‘terrestrial sterility’ of the newly discovered worlds of Saturn: a lesson learned from earlier lethal ‘first contacts’ in human history.

Cassini’s inspiring journey extended the outer limits of human understanding and consciousness to places far stranger than our wildest speculations. It has been an historic, even heroic undertaking. Cassini opened a previously hidden door to perplexing mysteries that hint at fresh insight and rich learning.